The present invention relates generally to fuel injectors, and more particularly to common rail systems with a three way control valve.
Common rail fuel injection systems offer an efficient, relatively simple means for pressurizing and injecting fuel in an internal combustion engine. These systems use a single pump to pressurize fuel, which is transferred to a common rail, from where it is distributed to the fuel injectors. Some of these systems not only inject diesel fuel, but also use fuel to directly control the opening and closing of valves within the injectors. One example of such a design is found in the BOSCH APCRS fuel system. Which is described in xe2x80x9cHeavy Duty Diesel Enginesxe2x80x94The Potential of Injection Rate Shaping for Optimizing Emissions and Fuel Consumptionxe2x80x9d, presented by Messrs. Bernd Mahr, Manfred Dxc3xcrnholz, Wilhelm Polach, and Hermann Grieshaber, Robert Bosch GmbH, Stuttgart, Germany, at the 21st International Engine Symposium, May 4-5, 2000, Vienna, Austria. The BOSCH system uses a medium pressure rail and a lift controlled injector with local intensification. Although the BOSCH APCRS and other common rail systems appear to function adequately, there is always room for improvement.
For example, the continuous fuel leakage during an injection causes a significant wastage of power. Engine power devoted to pressurizing fuel is wasted if high pressure fuel leaks out of the injector, reducing fuel efficiency. A further limitation is inherent in the manufacturing process used to make the BOSCH injectors. Because these injectors use several very small flow control orifices, they must be meticulously machined.
The present invention is directed to solving one or more of the problems or limitations set forth above.
A fuel injector is provided which includes an injector body defining a needle control chamber, a needle control vent, a nozzle chamber, a fuel inlet, and a nozzle outlet. A needle control valve is positioned in the injector body and includes a poppet control valve member. The poppet control valve member has a first position in which the needle control chamber is fluidly connected to the fuel inlet, but closed to the needle control vent, and a second position in which the needle control chamber is closed to the fuel inlet but open to the needle control vent. A needle valve member includes a closing hydraulic surface exposed to fluid pressure in the needle control chamber and an opening hydraulic surface exposed to fluid pressure in the nozzle chamber.
In another aspect, a fuel injection system is provided which includes a source of high pressure fuel, a low pressure fuel reservoir, and at least one fuel injector which has an injector body that defines a nozzle chamber, a needle control chamber, a needle control vent, a fuel inlet, and a nozzle outlet. A high pressure line extends between the source of high pressure fuel and the fuel inlet. A low pressure line extends between the low pressure fuel reservoir and the needle control vent. A needle control valve is positioned in the injector body and includes a poppet control valve member with a first position in which the needle control chamber is fluidly connected to the fuel inlet but closed to the needle control vent. The poppet control valve member also has a second position in which the needle control chamber is closed to the fuel inlet but open to the needle control vent. A needle valve member is positioned in the injector body and includes a closing hydraulic surface exposed to fluid pressure in the needle control chamber, and an opening hydraulic surface exposed to fluid pressure in the nozzle chamber.
In still another aspect, the present invention includes a method of injecting fuel which includes the step of relieving pressure on a closing hydraulic surface of a needle valve member. This is achieved at least in part by moving a poppet control valve member to a position that closes fluid communication between a common fuel rail and a needle control chamber. The method also includes the step of resuming pressure on the closing hydraulic surface at least in part by moving the poppet control valve member to a position that opens fluid communication between a common fuel rail and the needle control chamber.